Fix gst-plugins-base reference/requirement. This caused spurious
problems with uninstalled -ugly/-bad not finding -good plugins in
their unit tests (when distchecking).
Original commit message from CVS:
* Makefile.am:
* configure.ac:
* pkgconfig/.cvsignore:
* pkgconfig/Makefile.am:
* pkgconfig/gstreamer-plugins-good-uninstalled.pc.in:
add a .pc file so other modules can use good plugins in tests